The primary purpose of this project is to examine the long-term sensory and cognitive effects of prenatal exposure to methylmercury, a prevalent environmental pollutant. Twenty-three macaques were prenatally exposed environmentally relevant levels of methylmercury in the early 1980s and are now 15-17 years old. In the last twelve months we have completed tests of hearing on these animals and results indicate that prenatal exposure to methylmercury does not result in high-frequency hearing impairment. This finding suggests that postnatal exposure alone may be responsible for mercury-induced hearing deficits. All animals have now been trained on a spatial memory procedure and we are currently introducing the test phase of this experiment. Results will provide a rigorous examination of spatial memory, a type of memory known to be altered by the normal aging process. In addition, we have collected data on visual-spatial orientation and motor coordination during the past year. No evidence of treatment-related deficits on either task has been obtained thus far. Measurements of physical stature and weight continue to be collected routinely and females are observed daily for menstrual cycling. FUNDING NIH grants RR00166, ES037545, ES07033 and ES03745.